Crossing Situation - Risk of Collision and Action to Avoid Collision

This subject has come up recently on a couple threads here. Coaster Verity and Bulker Polesie Collide Off Helgoland and What navigation and ship handling skills (without instruments) should junior officer have?

In a crossing situation at what point is a course change to port by the give-way vessel contrary to the rules?

Good article at Safety4Sea by Harry Hirst here

Collisions at sea: Why are they still happening?

I have an older edition of Farwell’s (6th ED). It has this to say:

“Risk of collision begins the very moment when the two vessels have approached so near each other and upon such courses that by departure from the rules of navigation … a collision might be brought about”

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The most obvious answer that comes to mind when it places him in extremis with the stand-on vessel. An example would be a when the give-way vessel’s course takes him across the path of the stand-on vessel that is steaming from his right to his left and he turns to port with insufficient CPA.

When the other vessel is on the starboard bow, a turn to port seems likely to cross her course, but for a vessel closer to the beam a very large turn could be used to either turn circles or parallel the her course.

Cockcroft notes that with the other vessel off the starboard beam, a very large alteration (e.g. 60°) to port may be effective. There’s a comment in Farwell’s that includes a large alteration to port among viable options when in extremis.

My thinking would be, the further forward of the beam the stand-on vessel is located, the more likely a turn to port would be contrary to the rules. (Similarly, for those edge cases that approach head-on, turning to port would be a Bad Thing.) I do think a rules-compliant turn to port would also need to be quite significant, far more so than one might think sufficient to be “readily apparent”.

Rule 15 applies when :

-Vessels are in sight of eachother
-Risk of collision exists

Risk of collison exists:

-with Constant Bearing Decreaing range

So, I would say it would be contrary to the rules to alter course to port when you observe a red sidelight to starboard with a constant bearing.

Take with a grain of salt

I have found some guidance concerning this issue in an article by Craig H. Allen Sr Sep 26, 2012 “Be skeptical of rigid ‘in extremis’ dogma beyond ColRegs”.

I believe he provides some potential information as to the possible maneuver to port.

Using collision-inevitable position and the turning characteristics of the give-way vessel, there maybe a sound last resort reasoning as turn to port. Even though contrary to strict interpretation to the rules.

And what, precisely, in Rule 15 says that the give-way vessel cannot turn to port?

(a) When two Power Driven Vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.

If there is a vessel to starboard, and you are going to take early an substantial action, there is a “shall” there when it comes to avoiding crossing ahead. I can not think of any prudent turn to starboard in such a situation that would result in crossing ahead, or a prudent turn to port which would result in crossing astern, therefore it is a turn to port that is prohibited. Unless, the circumstances of the case do not permit, which would be special circumstances.

The range of the side lights is only 3 miles, at that point at 18 or 20 kts there’s already both risk of collision and a close-quarters situation. A turn should be made at least twice that distance. Even at 6 miles, in most circumstances, only a turn to starboard is going to be prudent.

From here

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That’s the fun part, Rules 11- 18 only apply to vessel in sight of one another. Until the COLREGS get their next refresh which should contain provision for unmanned vessels, electronic observation does not count as in sight, you must be able to see each other with your eyes. I know they must be so bright at 3 miles, however in practice side lights are visible well beyond 3 miles. If you can not see a vessel at 4 miles, and you can not maneuver to avoid collision a 20 knots, you are not proceeding at a safe speed. But in summary, yes, don’t turn left, unless you’re overtaking. If there is a vessel over the horizon on AIS that’s a crossing situation with 0 CPA, there is nothing against the rules in coming left.

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When will the winner be announced?

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A turn to port that neither crosses ahead, nor crosses astern, may buy space and time, after which a resumption of course could result in passing astern. I.e. turn enough that your courses now diverge, or (if the other vessel is particularly faster) at least are parallel.

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the issue is always when are you “in sight of each other” can you assume that if you see him, he can see you ? don’t think so - in a practical sense i always called it at somewhere around 6 miles or so -

interested if there is actully some real interpretaion on this

Take with a grain of salt.

Is there any consensus on use of the five stages process to determine “Risk of Collision” and “Action to Avoid Collision” in clear visibility.

Stage 1: free movement with long range (Not in visual sight beyond the horizon).

Stage 2: risk of collision exists. (Visually in-sight e.g., on the horizon or geographical range of ships lights)

Stage 3: close-quarters situation. (Range of or visual sighting of individual mast lights 6 NM)

Stage 4: immediate danger situation. (Range of or visual sighting of individual side lights 3 nm)

Stage 5: collision.

If he can’t see you, some of 1) an inadequate look-out, 2) operating per rule 19, or 3) no operating radar is in play. Which means he’s likely either to do nothing or turn to starboard.

Cockcroft acknowledges “in sight” may not be mutually simultaneous, and notes “A vessel must comply with the Rule which relates to the situation which applies at the particular instant”.

Farwell’s notes some difference in US vs English courts regarding re-assessment of roles/actions after passing from radar into visual range, but I would need to go back and give that section a re-read.

Hirst’s book spends time discussing a few cases, and differentiates types of variable visibility; i.e. vertically variable where some of the other vessel’s lights are obscured by fog, and horizontally variable where you can catch sight for brief periods. Of course, this is slightly different from one vessel having a clear visual and the other not.

The OP links to another thread - the turn to port was for a group of near by F/Vs, not a turn to port for the more distant (12 miles) deep-sea stand-on vessel.

In response to this thread - I was suggesting that Craig Allen’s Article “Be skeptical of rigid ‘in extremis’ dogma beyond ColRegs” presented a possible consideration for the prudent mariner as to the traditional turn to the right by the give-way vessel.

“Lott’s recommended extremis maneuver was, not surprisingly today, a course change to the right. Indeed, at about the same time, the U.S. Second Circuit Court of Appeals opined that “it is indeed the instinctive response of a master in an emergency to put his rudder hard right.” While it might be an instinctive response, it is not always a prudent choice.”

The article seems to present a possible case where a change to port by the give-way vessel may not necessarily be contrary to the rules.

From observation (deep-sea ships at sea speed) turning at around 6 miles seems to be common practice. At 20 kts 6 miles is covered in 18 minutes.

Harry Hirst recommends rather than thinking in terms of distance, think instead in terms of time. Rather then just distance of CPA think also about avoiding a close-quarters situation.

Hirst suggests a close-quarters situation is a TCPA of 12 minutes or less (4 miles at 20 kts).

The standard practice to alter at 6 miles (18 minutes at 20 kts) to a course that will result in passing at a safe distance will in most cases comply with the requirement that actions to avoid collision be taken in ample time.

I started using TCPA of 18 minutes in my standing orders after another member mentioned it on this forum.

agree - part of the problem I posted on the other thread was to just avoid all the traffic being in the same place in 20-30 min. IMO one of the best uses of radar that junior officers need to learn is to be looking ahead an hour or two and see if there is anything you can do very early that keeps you out of that situation.

As an example - on our normal run we would encounter the fishing vessels off the coast of florida. If it was my watch I would often call the Captain an hour or two before we would be in them and ask him if he wanted to spend some time on the bridge later tonight, or would he prefer i just turn now, add some time to our trip, and avoid them all.


The five stages in that article was for the purpose of discussing risk of collision and the range of a vessel’s running lights. The general concept of stages is valid but the actual specific distances is going to vary according to circumstances.